There was a ton of excellent commentary on my previous post (which I encourage you to check out…Kalon wrote more in my comments in a day than he’s written on his blog in a month). As such, let me try to clarify a bit.

The Hybrid Spec…when would you use it?

I basically see three situations where having a hybrid CatBear spec (as opposed to a CatUtility spec, which I’d generally recommend) would be useful.

The MT dies, and a fillin MT is needed. Typically, a tank death means a wipe in 10-man, and usually in 25-man. Raids don’t carry a “just-in-case” tank, and by the time the MT gets a rez, enough of the raid is dead that it doesn’t matter. (Either that, or it’s one of those bosses that splits his damage between two tanks or has a stacking debuff, which means your second tank is taking a ton of damage and dying quite quickly.) Having a cat that can go bear can prevent this wholesale carnage by holding aggro on the boss, not dying immediately (by cooldown usage) and giving time for a MT rez and a healer adjustment. Obviously, in this scenario, you won’t be PLANNING on the tank dying, so you’ll be in your cat gear and glyphs. You won’t be an optimal tank, but you’re much better than anyone else. (I have an addon that gives me a distinct audio cue when the tank dies. I’ve trained myself to automatically go bear when I hear that, as I will typically be pretty high on the threat list anyway.)
Now, opinons vary on the longterm viability of a CatBear emergency tank (say the rez already got used on the healer, so you’re all that’s left from 50%-0%). You’ll have less stamina than a regular tank does, because you won’t have tank trinkets/jewelry. You’ll take a bit more damage, because you won’t have the tanking meta. It’s not all bad, though- your avoidance will be slightly higher than a regular tank, because of your higher agility, and you shouldn’t have any problems with threat because you’re in DPS gear. In my mind, the viability of this is directly related to your raid’s level (norm/heroic), size, and encounter type. In a 25H, for example, simply because the boss outputs so much damage that you’ll likely die before your healers can adjust, and even if they do, you’re very susceptible to burst. In a 10M, surviving this is much more likely. Of course, if it’s a dragon fight that revolves around surviving burst, you’re likely dead anyway. (A lot of this thinking is based around LK health pools. If burst is less of a concern in Cata, then that makes a hybrid build more attractive.)

A fight demands a temporary OT (adds, stacking debuff on MT, etc) and has a tight DPS requirement. These type of fights aren’t very common, but this is the perfect scenario for the CatBear spec. For an example, I remember reading about a world top10 10-strict guild who got their first kill of H Sindragosa by using a cat-specced druid tanking Sindy to let the debuff drop off the MT. (I want to say this was Kae’s guild, but I’m not sure.) I’ve deliberately been avoiding reading too many details about Cataclysm bosses, so I don’t know how many encounters will be similar to that.

5-man/entry-level-raid pugging. This is somewhat similar to point 1, but if you have a poor tank (or a tank leaves, etc), you can step in for them and tank without any interruption. You being somewhat sub-optimal is made up for the fact that you’re running non-progression content, and there’s a very real risk that the group/raid will disband if people have to wait for you to go respec. Of course, you could dual spec feral for this, which I’m not opposed to at all. I do like playing resto as well, however, and I’m ready to step in if we lose a healer (again, without needing to go run and respec, which can break a PUG).

Other than those situations, I’d prefer the CatUtility spec (or a full Bear spec, depending on the situation) I recommended in my feral DPS guide. As Kalon noted, porting to Moonglade to respec is pretty quick, so it takes hardly any time in an organized run to go optimize. Pretty much, as the content you’re attempting gets more difficult/specialized (N->H, 10->25, T11->T12->T13), the deficiencies of the hybrid build become more prevalent. Of course, this depends on your guild as well. If your tanks tend to die a lot, then you might want to consider it more (or go resto. :))

Personally, I’ll probably do the same thing I did for WOTLK; run a hybrid build for leveling/5-mans/entry-level raiding, then re-evaluate. (I think I re-specced to a full Cat build for the first time somewhere in Ulduar. Of course, I was in a much more casual guild then.) Once Rawr gets updated for Cata and we start to see some more complete gear information, I can actually get some hard numbers about the survivability of a fully specced/geared bear vs. a moonlighting cat.